WO2013146819A1

WO2013146819A1 - Secondary battery

Info

Publication number: WO2013146819A1
Application number: PCT/JP2013/058865
Authority: WO
Inventors: 信作齊藤; 井上　和彦
Original assignee: 日本電気株式会社
Priority date: 2012-03-29
Filing date: 2013-03-26
Publication date: 2013-10-03
Also published as: JPWO2013146819A1; JP6086116B2

Abstract

The present invention relates to: an electrolyte solution for lithium secondary batteries, which contains a sulfonic acid ester compound and a compound that has two or more unsaturated bonds at ends; and a lithium secondary battery which uses the electrolyte solution for lithium secondary batteries.

Description

Secondary battery

The present invention relates to an electrolytic solution for a secondary battery and a secondary battery using the same.

With the rapid market expansion of notebook computers, mobile phones, electric vehicles, etc., secondary batteries with high energy density are required. Examples of means for obtaining a high energy density secondary battery include a method using a negative electrode material having a large capacity, a method using a non-aqueous electrolyte having excellent stability, and the like.

In the lithium secondary battery, a carbonate-based solvent such as ethylene carbonate (EC) is preferably used. However, for example, when a carbon material such as graphite is used for the negative electrode, there is a problem in that the electrolytic solution is decomposed at the negative electrode and the battery characteristics are deteriorated.

Patent Documents

1 and 2 disclose an electrolytic solution containing a disulfonic acid ester derivative as an additive in order to improve battery cycle characteristics, electric capacity, and the like.

JP 2000-133304 A JP 2001-313071 A

However, in the secondary battery using the electrolytic solution described in

Patent Documents

1 and 2, both the capacity retention ratio and the discharge capacity when many cycles are repeated are insufficient. In the examples of Patent Document 1 and Patent Document 2, only the case where one kind of additive is used in the electrolytic solution is shown.

The present invention relates to an electrolytic solution for a lithium secondary battery including a sulfonic acid ester compound and a compound having two or more unsaturated bonds at the terminal, and a secondary battery using the same.

According to the present invention, a lithium secondary battery with improved cycle characteristics can be obtained.

It is a schematic block diagram of the laminated exterior type | mold structure of the nonaqueous electrolyte secondary battery of this invention.

The configuration of a secondary battery using the non-aqueous electrolyte of the present invention will be described with reference to the drawings. FIG. 1 is an example of a schematic configuration diagram of a secondary battery using the nonaqueous electrolytic solution of the present invention. The battery according to the present invention has a structure as shown in FIG. The positive electrode is formed by forming a layer 1 containing a positive electrode active material on a positive electrode current collector 3. The negative electrode is formed by forming a layer 2 containing a negative electrode active material on a negative electrode current collector 4. These positive electrode and negative electrode are arranged to face each other with a porous separator 5 interposed therebetween. The porous separator 5 is disposed substantially parallel to the layer 2 containing the negative electrode active material. In the secondary battery of the present invention, the electrode element in which the positive electrode and the negative electrode are arranged to face each other, and the electrolytic solution are included in the exterior bodies 6 and 7. The shape of the non-aqueous electrolyte secondary battery according to the present embodiment is not particularly limited, and examples thereof include a laminate exterior type, a cylindrical type, a square type, and a coin type.

<Electrolyte>
The electrolyte solution in this embodiment contains a sulfonic acid ester compound and a compound having two or more unsaturated bonds at the ends as additives in the non-aqueous electrolyte solution.

The non-aqueous electrolyte is not particularly limited, and for example, a solution in which a lithium salt is dissolved in a non-aqueous solvent can be used.

Examples of the lithium salt include LiPF ₆ , lithium imide salt, LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF _{6, and the} like. The lithium imide _{_{_{_{salt, LiN (C k F 2k +}}}} 1 SO 2) (C m F 2m + 1 SO 2) (k and m are each independently 1 or 2). These may use only 1 type and may use 2 or more types together.

As the non-aqueous solvent, at least one solvent selected from the group consisting of cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, γ-lactones, cyclic ethers and chain ethers can be used. Examples of the cyclic carbonate include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and derivatives thereof (including fluorinated products). Examples of the chain carbonate include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC), and derivatives thereof (including fluorinated products). Examples of the aliphatic carboxylic acid ester include methyl formate, methyl acetate, ethyl propionate, and derivatives thereof (including fluorinated products). Examples of γ-lactone include γ-butyrolactone and its derivatives (including fluorinated products). Examples of the cyclic ether include tetrahydrofuran, 2-methyltetrahydrofuran and derivatives thereof (including fluorinated products). Examples of the chain ether include 1,2-diethoxyethane (DEE), ethoxymethoxyethane (EME), ethyl ether, diethyl ether, and derivatives thereof (including fluorinated compounds). Other non-aqueous solvents include dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propyl nitrile, nitromethane, ethyl monoglyme, phosphate triester, trimethoxymethane, Dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, 1,3-propane sultone, anisole, N-methylpyrrolidone, and derivatives thereof (fluorinated compounds) Can also be used. These may use only 1 type and may use 2 or more types together.

The concentration of the lithium salt in the nonaqueous electrolytic solution is preferably 0.7 mol / L or more and 1.5 mol / L or less. By setting the concentration of the lithium salt to 0.7 mol / L or more, sufficient ionic conductivity can be obtained. Moreover, by making the density | concentration of lithium salt 1.5 mol / L or less, a viscosity can be made low and the movement of lithium ion is not prevented.

In the present embodiment, a sulfonic acid ester compound (hereinafter sometimes referred to as “compound A”) as an additive in the non-aqueous electrolyte and a compound having two or more unsaturated bonds at the terminals ( Hereinafter, it may be described as “compound B”). In the present specification, when simply described as “sulfonic acid ester compound” or “compound A”, a compound having two or more unsaturated bonds at the terminal is not included unless otherwise specified.

(Compound A)
The sulfonate compound (compound A) in the present embodiment has at least one —SO ₂ —O— structure, and in one —SO ₂ —O— structure, the S atom includes three O atoms, a carbon atom, And one O atom is bonded to an S atom and a carbon atom. Of these, the sulfonic acid ester compound preferably includes one or more —SO ₂ —O— structures and one or more alkyl groups and / or alkylene chains, and —SO ₂ —O— structure, It is more preferable that the alkyl group and / or the carbon of the alkylene chain are directly bonded, and it is further more preferable that the —SO ₂ —O— structure consists only of the alkyl group and / or the alkylene chain. The alkyl group is present as a terminal group when the sulfonate compound is in a chain form. The alkylene chain is present as a linking group between the sulfonate compound when it contains two or more —SO ₂ —O— structures or when it is a cyclic structure. By containing Compound A in the electrolytic solution, a film that prevents the reduction reaction of the electrolytic solution can be formed on the negative electrode surface.

In the present embodiment, the sulfonic acid ester compound may have a chain structure or a cyclic structure, but is preferably a cyclic structure because the reactivity on the negative electrode surface is improved. In addition, the sulfonic acid ester compound may have one or more —SO ₂ —O— structures, but having two or more is preferable because reactivity on the negative electrode surface is improved. For example, —SO ₂ —O— A disulfonic acid ester compound having two structures is more preferable. In the present embodiment, for example, a cyclic disulfonic acid ester compound represented by the following formula (1) is preferable, and a compound in which R1 and R2 are methylene groups in the formula (1) is more preferable. In the electrolytic solution, compound A may be used alone or in combination of two or more.

(In the formula, R 1 and R 2 are each independently an alkylene chain having 1 to 5 carbon atoms.)

(Compound B)
The compound (compound B) having two or more unsaturated bonds at the terminals in this embodiment includes two or more unsaturated bonds that are double bonds or triple bonds at the terminals of the molecule. The unsaturated bond is preferably a carbon-carbon unsaturated bond. By having an unsaturated bond in the molecule, when the negative electrode contains carbon, the affinity for the carbon negative electrode is improved and adsorption is facilitated. In addition, since compound B is polymerized on the negative electrode, even if expansion and contraction of the active material due to charge / discharge occurs, it is difficult to peel off from the active material surface, so that a stable film can be formed.

As the compound B, for example, a sulfonic acid ester compound having two or more unsaturated bonds at the terminal is preferable. The sulfonic acid ester compound having two or more unsaturated bonds at the terminal in the present embodiment has two or more unsaturated bonds at the terminal, has at least one —SO ₂ —O— structure, and one —SO ₂ —. In the O-structure, S atoms are bonded to three O atoms and carbon atoms, and one O atom is bonded to S atoms and carbon atoms. Of these, compound B preferably contains two or more unsaturated bonds, one or more —SO ₂ —O— structures, and one or more alkyl groups and / or alkylene chains, More preferably, the ₂ —O— structure and the alkyl group and / or carbon of the alkylene chain are directly bonded, and two or more unsaturated bonds, the —SO ₂ —O— structure, the alkyl group and / or Or it is more preferable that it consists only of an alkylene chain. The alkyl group is present as an end group when the compound B is a chain.

The sulfonic acid ester compound having two or more unsaturated bonds at the terminal may have one or more —SO ₂ —O— structures, but preferably has two or more. In the present embodiment, for example, a disulfonic acid ester compound having two double bonds represented by the following formula (2) is preferable, and a bisallylmethanesulfonic acid ester in which R3 is a methylene group in the following formula is more preferable.

(Wherein R3 is an alkylene chain having 1 to 5 carbon atoms.)

Examples of compounds having two or more unsaturated bonds at the terminals other than the above (compound B) include, for example, 1,3,5-triethynylbenzene represented by the following formula (3-1), represented by the formula (3-2) Tripropargylamine, triallyl isocyanurate (TAIC) represented by formula (3-3), triallyl cyanurate (TAC) represented by formula (3-4), and formula (3-5) And tetraallylpentaerythrulphonic acid ester, and trialkynylphosphonic acid ester represented by the formula (3-6). In the electrolytic solution, Compound B may be used alone or in combination of two or more.

As described above, in the present embodiment, the electrolyte includes the sulfonic acid ester compound (Compound A) and the compound having two or more unsaturated bonds (Compound B) as additives. When compound A and compound B are used in combination, compound B can form a cross-linked structure by having two or more unsaturated bonds in the molecule, thereby further stabilizing the film that prevents the reduction reaction of the electrolyte formed by compound A. Can be

In the present embodiment, the compound A and the compound B each preferably have a —SO ₂ —O— structure, although not particularly limited. When Compound A and Compound B have the same —SO ₂ —O— structure, the affinity between Compound A and Compound B is improved, so that adsorption to the negative electrode surface can be induced. And, by improving the affinity between the compound A and the compound B, the crosslinked structure of the compound B and the film of the compound A form a uniform composite film, so that lithium ions can permeate the film uniformly, Smooth insertion and removal from the active material. This reduces the internal resistance and reduces the damage to the active material, thereby improving the battery life. In this embodiment, for example, it is preferable to use a disulfonic acid ester compound as the compound A and a sulfonic acid ester compound having two double bonds as the compound B, and the cyclic disulfonic acid ester represented by the above formula (1) It is more preferable to use the compound and a disulfonic acid ester compound having two double bonds at the terminal represented by the formula (2) in combination.

The total content of Compound A and Compound B is not particularly limited, but is preferably 0.01 mol / L or more and 0.2 mol / L or less, more preferably 0.03 mol / L or more and 0.2 mol / L or less in the electrolytic solution. Preferably, 0.1 mol / L is particularly preferable. The mixing ratio of compound A and compound B is not particularly limited, but is preferably 1: 9 to 9: 1.

In the present embodiment, the electrolyte solution may contain other additives other than the compound A and the compound B as necessary. Examples of other additives include an overcharge inhibitor, a surfactant, and a gelling agent.

<Negative electrode>
The negative electrode can be produced by forming a negative electrode active material layer containing a negative electrode active material and a negative electrode binder on a negative electrode current collector. In the nonaqueous electrolyte secondary battery of FIG. 1, the negative electrode active material used for the layer 2 containing the negative electrode active material is selected from the group consisting of, for example, lithium metal, a lithium alloy, and a material capable of inserting and extracting lithium. One or more substances can be used. As a material for inserting and extracting lithium ions, a carbon material or an oxide can be used.

As the carbon material, graphite that absorbs lithium, amorphous carbon, diamond-like carbon, carbon nanotubes, or a composite oxide thereof can be used. Of these, graphite material or amorphous carbon is particularly preferable. In particular, the graphite material has high electron conductivity, excellent adhesion to a current collector made of a metal such as copper, and voltage flatness, and is formed at a high processing temperature, so it contains few impurities and has negative electrode performance. It is advantageous for improvement and is preferable. As the oxide, any of silicon oxide, tin oxide, indium oxide, zinc oxide, lithium oxide, phosphorus oxide (phosphoric acid), boric oxide (boric acid), or a composite thereof may be used. In particular, it is preferable to include silicon oxide. The structure is preferably in an amorphous state. This is because silicon oxide is stable and does not cause a reaction with other compounds, and the amorphous structure does not lead to deterioration due to nonuniformity such as crystal grain boundaries and defects.

The lithium alloy is composed of lithium and a metal capable of forming an alloy with lithium. For example, it is composed of a binary or ternary alloy of a metal such as Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La, and lithium. . As the lithium metal or lithium alloy, an amorphous one is particularly preferable. This is because the amorphous structure hardly causes deterioration due to non-uniformity such as crystal grain boundaries and defects. Lithium metal or lithium alloy is formed by an appropriate method such as a melt cooling method, a liquid quenching method, an atomizing method, a vacuum deposition method, a sputtering method, a plasma CVD method, a photo CVD method, a thermal CVD method, a sol-gel method, etc. Can do.

Examples of the binder for the negative electrode include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene copolymer rubber, polytetrafluoroethylene, polypropylene, polyethylene, Polyimide, polyamideimide, or the like can be used. The amount of the binder for the negative electrode used is 0.5 to 25 parts by mass with respect to 100 parts by mass of the negative electrode active material from the viewpoints of “sufficient binding force” and “high energy” which are in a trade-off relationship. Is preferred.

As the negative electrode current collector, aluminum, nickel, copper, silver, and alloys thereof are preferable in view of electrochemical stability. Examples of the shape include foil, flat plate, and mesh.

The negative electrode can be produced by forming a negative electrode active material layer containing a negative electrode active material and a negative electrode binder on a negative electrode current collector. Examples of the method for forming the negative electrode active material layer include a doctor blade method, a die coater method, a CVD method, and a sputtering method. After forming a negative electrode active material layer in advance, a thin film of aluminum, nickel, copper, silver, or an alloy thereof may be formed by a method such as vapor deposition or sputtering to form a negative electrode current collector.

In the negative electrode of the secondary battery in FIG. 1, a complex composed of a transition metal cation and an imide anion may be present at the interface with the non-aqueous electrolyte. The negative electrode is preferable because it is excellent in flexibility with respect to volume change of the metal and alloy phases, uniformity of ion distribution, and physical and chemical stability. As a result, dendrite formation and lithium atomization can be effectively prevented, and cycle efficiency and life are improved. Further, when a carbon material or an oxide material is used as the negative electrode, dangling bonds existing on the surface have high chemical activity, and the solvent is easily decomposed. By adsorbing a complex composed of a transition metal cation and an imide anion on this surface, the decomposition of the solvent is suppressed and the irreversible capacity is greatly reduced, so that the charge / discharge efficiency can be kept high. Furthermore, when the film is mechanically broken, lithium fluoride, which is a reaction product of lithium on the negative electrode surface and imide anion adsorbed on the negative electrode surface, has a function of repairing the film. Even after the film is destroyed, it has the effect of leading to the formation of a stable surface compound.

<Positive electrode>
In the secondary battery of FIG. 1, examples of the positive electrode active material used for the layer 1 containing the positive electrode active material include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ . In addition, the transition metal portion of these lithium-containing composite oxides may be replaced with another element. Alternatively, a lithium-containing composite oxide having a plateau at 4.2 V or higher at the metal lithium counter electrode potential can be used. Examples of the lithium-containing composite oxide include spinel-type lithium manganese composite oxide, olivine-type lithium-containing composite oxide, and reverse spinel-type lithium-containing composite oxide. The lithium-containing composite oxide can be, for example, a compound represented by the following formula (4).
Li _a (M _x Mn _2-x ) O ₄ (4)
(In Formula (4), 0 <x <2 and 0 <a <1.2. M is at least selected from the group consisting of Ni, Co, Fe, Cr, and Cu) It is a kind.)

In the positive electrode, these active materials are dispersed and kneaded in a solvent such as N-methyl-2-pyrrolidone (NMP) together with a conductive material such as carbon black and a binder such as polyvinylidene fluoride (PVDF). Can be obtained by coating on a positive electrode current collector such as an aluminum foil.

As a secondary battery manufacturing method, the secondary battery manufacturing method in FIG. 1 will be described as an example. The non-aqueous electrolyte secondary battery of FIG. 1 has a negative electrode and a positive electrode laminated via a porous separator 5 in a dry air or inert gas atmosphere. It accommodates in exterior bodies, such as a flexible film which consists of a laminated body of resin and metal foil, and is impregnated with the nonaqueous electrolyte solution containing the said compound A and compound B as an additive. And after sealing or sealing an exterior body, a favorable membrane | film | coat can be formed on a negative electrode by charging a nonaqueous electrolyte secondary battery. In addition, as the porous separator 5, porous films, such as polyolefin, such as a polypropylene and polyethylene, a fluororesin, are used. The exterior body can be appropriately selected as long as it is stable to the electrolytic solution and has a sufficient water vapor barrier property. For example, in the case of a laminated laminate type secondary battery, a laminate film made of aluminum, silica-coated polypropylene, polyethylene, or the like can be used as the outer package. In particular, it is preferable to use an aluminum laminate film from the viewpoint of suppressing volume expansion.

Hereinafter, the present embodiment will be specifically described by way of examples.

<Example 1>
(Production of battery)
The production of the battery of this example will be described. An aluminum foil having a thickness of 20 μm was used as the positive electrode current collector, and LiMn ₂ O ₄ was used as the positive electrode active material. Further, a 10 μm thick copper foil was used as the negative electrode current collector, and graphite was used as the negative electrode active material on the copper foil. And the negative electrode and the positive electrode were laminated | stacked through the separator which consists of polyethylene, and the secondary battery was produced.

(Preparation of non-aqueous electrolyte)
A mixed solvent of EC and DEC (volume ratio: 30/70) was used as a solvent for the nonaqueous electrolytic solution, and LiPF ₆ was dissolved at 1 mol / L as a supporting electrolyte.

As the sulfonic acid ester compound, 0.025 mol / L of a cyclic disulfonic acid ester (hereinafter referred to as “compound A1”) represented by the formula (1) and each of R1 and R2 is a methylene group, and two or more at the terminal 0.075 mol / L of a bisallylmethanesulfonic acid ester (hereinafter referred to as “compound B1”) represented by the formula (2) and having R3 as a methylene group is added as a compound having an unsaturated bond of It was set to 0.1 mol / L. A non-aqueous secondary battery was produced using the non-aqueous electrolyte to which these additives were added, and a charge / discharge cycle test was performed 500 cycles.

In the charge / discharge cycle test, the temperature of the thermostatic chamber is set to 55 ° C., and the charge / discharge conditions are CCCV charge rate 1.0C, CC discharge rate 1.0C, charge end voltage 4.2V, and discharge end voltage 3.0V. Discharge 500 cycles were performed. The ratio of the discharge capacity after 500 cycles to the initial discharge capacity was calculated as the capacity retention rate (%). Table 1 shows the results of the discharge capacity after 500 cycles and the capacity retention rate.

<Example 2>
As additives used in the non-aqueous electrolyte, 0.05 mol / L of compound A1, 0.05 mol / L of compound B1 were added, and the total mixed concentration was changed to 0.1 mol / L. A secondary battery was prepared and a charge / discharge cycle test was performed 500 cycles. The results are shown in Table 1.

<Example 3>
As additives used in the non-aqueous electrolyte, 0.075 mol / L of compound A1 and 0.025 mol / L of compound B1 were added, and the total mixed concentration was changed to 0.1 mol / L. A secondary battery was prepared and a charge / discharge cycle test was performed 500 cycles. The results are shown in Table 1.

<Example 4>
As additives used in the nonaqueous electrolyte, 0.025 mol / L of compound A1, 0.025 mol / L of compound B1 were added, and the total mixed concentration was 0.05 mol / L. A secondary battery was prepared and a charge / discharge cycle test was performed 500 cycles. The results are shown in Table 1.

<Example 5>
As additives used in the non-aqueous electrolyte, 0.1 mol / L of compound A1, 0.1 mol / L of compound B1 were added, and the total mixed concentration was changed to 0.2 mol / L. A secondary battery was prepared and a charge / discharge cycle test was performed 500 cycles. The results are shown in Table 1.

<Comparative Example 1>
A secondary battery was prepared in the same manner as in Example 1 except that Compound A1 was not added and Compound B1 was added in an amount of 0.025 mol / L as an additive used in the non-aqueous electrolyte, and the charge / discharge cycle test was performed 500 cycles. It was. The results are shown in Table 1.

<Comparative example 2>
A secondary battery was prepared in the same manner as in Example 1 except that Compound A1 was not added and Compound B1 was added in an amount of 0.05 mol / L as an additive used in the non-aqueous electrolyte, and the charge / discharge cycle test was performed 500 cycles. It was. The results are shown in Table 1.

<Comparative Example 3>
A secondary battery was prepared in the same manner as in Example 1 except that Compound A1 was not added and Compound B1 was added in an amount of 0.1 mol / L as an additive used in the non-aqueous electrolyte, and the charge / discharge cycle test was performed 500 cycles. It was. The results are shown in Table 1.

<Comparative Example 4>
A secondary battery was prepared in the same manner as in Example 1 except that Compound A1 was not added and Compound B1 was added in an amount of 0.15 mol / L as an additive used in the non-aqueous electrolyte, and the charge / discharge cycle test was performed 500 cycles. It was. The results are shown in Table 1.

<Comparative Example 5>
A secondary battery was prepared in the same manner as in Example 1 except that Compound A1 was not added and Compound B1 was added in an amount of 0.2 mol / L as an additive used in the non-aqueous electrolyte, and the charge / discharge cycle test was performed 500 cycles. It was. The results are shown in Table 1. In this comparative example, the electrolyte solution viscosity was increased by containing Compound B1 at a high concentration, and the amount of gas generation increased, making measurement impossible.

<Comparative Example 6>
A secondary battery was prepared in the same manner as in Example 1 except that Compound A1 was added at 0.025 mol / L and Compound B1 was not added as an additive used in the non-aqueous electrolyte, and the charge / discharge cycle test was performed 500 cycles. It was. The results are shown in Table 1.

<Comparative Example 7>
A secondary battery was prepared in the same manner as in Example 1 except that 0.05 mol / L of compound A1 was added and no compound B1 was added as an additive used in the non-aqueous electrolyte, and the charge / discharge cycle test was performed 500 cycles. It was. The results are shown in Table 1.

<Comparative Example 8>
A secondary battery was prepared in the same manner as in Example 1 except that 0.1 mol / L of compound A1 was added and no compound B1 was added as an additive used in the nonaqueous electrolytic solution, and the charge / discharge cycle test was performed 500 cycles. It was. The results are shown in Table 1.

<Comparative Example 9>
A secondary battery was prepared in the same manner as in Example 1 except that 0.15 mol / L of compound A1 was added and no compound B1 was added as an additive used in the non-aqueous electrolyte, and the charge / discharge cycle test was performed 500 cycles. It was. The results are shown in Table 1.

<Comparative Example 10>
A secondary battery was prepared in the same manner as in Example 1 except that Compound A1 and Compound B1 were not added as additives used in the nonaqueous electrolytic solution, and a charge / discharge cycle test was performed 500 cycles. The results are shown in Table 1.

(Evaluation results of cycle test)
As described above, for the purpose of improving the charge / discharge cycle life, 1 mol / L of LiPF ₆ is added as a supporting electrolyte in a mixed solvent of EC and DEC (volume ratio: 30/70) as a solvent of the nonaqueous electrolytic solution, Further, a cycle test was conducted using additives (Examples 1 to 5) in which the mixing ratio of Compound A1 and Compound B1 was allocated as an additive. The case where only compound A1 was mixed as a comparison target (Comparative Examples 6 to 9), the case where only Compound B1 was mixed (Comparative Examples 1 to 5), or the case where neither Compound A1 nor Compound B1 was mixed (Comparative Example 10) A cycle test was conducted.

When comparing Examples 1 to 5 and Comparative Examples 1 to 10, both the discharge capacity and the capacity retention rate are higher in Examples 1 to 5. On the other hand, when Comparative Examples 1 to 9 and Comparative Example 10 are compared, even when only Compound A1 or Compound B1 alone is used, the effect of improving the cycle life is better than when no additive is used. is there. However, as shown in Examples 1 to 5, it was found that the effect of improving the cycle life was remarkable when Compound A1 and Compound B1 were used in combination. In addition, when 1 mol of Compound A1 and 0.05 mol / L of Compound B1 are added in 1 L of electrolyte solution, and the total is 0.1 mol / L, it is shown that the cycle life is particularly effective. It was.

DESCRIPTION OF SYMBOLS 1 Positive electrode active material layer 2 Negative electrode active material layer 3 Positive electrode collector 4 Negative electrode collector 5 Porous separator 6 Laminate exterior body 7 Laminate exterior body 8 Negative electrode tab 9 Positive electrode tab

Claims

An electrolyte solution for a lithium secondary battery, comprising a sulfonic acid ester compound and a compound having two or more unsaturated bonds at the terminal.
The electrolyte solution for a lithium secondary battery according to claim 1, wherein the sulfonic acid ester compound is a disulfonic acid ester compound.
The electrolyte solution for a lithium secondary battery according to claim 1 or 2, wherein the sulfonic acid ester compound is a cyclic disulfonic acid ester compound.
The electrolyte for a lithium secondary battery according to any one of claims 1 to 3, wherein the compound having two or more unsaturated bonds at the terminal is a sulfonate compound having two or more unsaturated bonds at the terminal. liquid.
The electrolyte for a lithium secondary battery according to any one of claims 1 to 4, wherein the compound having two or more unsaturated bonds at the terminal is a disulfonic acid ester compound having two or more unsaturated bonds at the terminal. liquid.
6. The lithium secondary battery according to claim 1, wherein the total of the sulfonic acid ester compound and the compound having two or more unsaturated bonds at the terminal is 0.03 to 0.2 mol / L. Secondary battery electrolyte.
7. The lithium secondary battery according to claim 1, wherein a ratio of the sulfonic acid ester compound to the compound having two or more unsaturated bonds at the terminal is 1: 9 to 9: 1. Electrolytic solution.
The sulfonic acid ester compound is represented by the following formula (1):

(In the formula, R 1 and R 2 are each independently an alkylene chain having 1 to 5 carbon atoms.)
A compound represented by
The compound having two or more unsaturated bonds at the terminal is represented by the following formula (2):

(Wherein R3 is an alkylene chain having 1 to 5 carbon atoms.)
The electrolyte solution for a lithium secondary battery according to any one of claims 1 to 7, which is a compound represented by the formula:
The electrolyte solution for a lithium secondary battery according to any one of claims 1 to 8, further comprising 1M LiPF 6 as a supporting salt.
A lithium secondary battery comprising the electrolyte solution for a lithium secondary battery according to any one of claims 1 to 9.